On Tue, Feb 26, 2019 at 1:54 PM Rob Herring <robh@xxxxxxxxxx> wrote:
>
> On Sun, Feb 24, 2019 at 08:27:23AM +0000, Pankaj Bansal wrote:
> > This adds device tree binding documentation for generic register based
> > multiplexer controlled by a bitfields in a parent device's register range.
> >
> > Signed-off-by: Pankaj Bansal <pankaj.bansal@xxxxxxx>
> > ---
> >
> > Notes:
> > V3:
> > - Added the patch in series with the driver patch
> > - Fixed the node value out of bitfield error
> > - removed the "parent register r/w functions" line
> > V2:
> > - Removed syscon reference from txt file
> > - Removed loading zeroes from hex numbers
> > - Fixed the depth of dts nodes
> > - fixed minor formatting errors
> >
> > .../devicetree/bindings/mux/reg-mux.txt | 83 ++++++++++++++++++
> > 1 file changed, 83 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/mux/reg-mux.txt b/Documentation/devicetree/bindings/mux/reg-mux.txt
> > new file mode 100644
> > index 000000000000..8bea6129c113
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/mux/reg-mux.txt
> > @@ -0,0 +1,83 @@
> > +Generic register bitfield-based multiplexer controller bindings
> > +
> > +Define register bitfields to be used to control multiplexers. The parent
> > +device tree node must be a device node to provide register r/w access.
>
> We generally avoid register bit level bindings like this...
>
> What happens when I need 8 or 16-bit accesses. Or some quirky encoding
> of the bits. Or non-contiguous bit fields... It's an endless extending
> of the binding to try to handle different cases.
I think the intention here is to mimic the existing mmio-mux binding
(Documentation/devicetree/bindings/mux/mmio-mux.txt) so that the
existing mmio-mux driver can be extended to cover both MMIO and
non-MMIO register based muxes. The bit-width of the register access
will be taken care of by the regmap framework. It is probably true
that this can not cover all the register based mux device if they do
have quircky register layout, but I think it should be good enough to
cover majority of the cases. If there are devices that cannot be
covered by the generic binding and driver, they could create their own
bindings and drivers.
>
> > +
> > +Required properties:
> > +- compatible : "reg-mux"
> > +- #mux-control-cells : <1>
> > +- mux-reg-masks : an array of register offset and pre-shifted bitfield mask
> > + pairs, each describing a single mux control.
> > +* Standard mux-controller bindings as decribed in mux-controller.txt
> > +
> > +Optional properties:
> > +- idle-states : if present, the state the muxes will have when idle. The
> > + special state MUX_IDLE_AS_IS is the default.
> > +
> > +The multiplexer state of each multiplexer is defined as the value of the
> > +bitfield described by the corresponding register offset and bitfield mask pair
> > +in the mux-reg-masks array.
> > +
> > +Example:
> > +
> > +&i2c0 {
> > + fpga@66 { // fpga connected to i2c
> > + compatible = "fsl,lx2160aqds-fpga", "fsl,fpga-qixis-i2c",
> > + "simple-mfd";
> > + reg = <0x66>;
> > +
> > + mux: mux-controller { // Mux Producer
> > + compatible = "reg-mux";
>
> > + #mux-control-cells = <1>;
> > + mux-reg-masks = <0x54 0xf8>, /* 0: reg 0x54, bits 7:3 */
> > + <0x54 0x07>; /* 1: reg 0x54, bits 2:0 */
>
> You can accomplish the same thing by moving these 2 properties to the
> parent. The parent driver can register a generic mux if that's
> appropriate.
Again, the intention is to reuse the generic mux binding and driver.
Regards,
Leo
